Photoelectric scanning device for generating musical tones



June 21, 1960 M. CLARK, JR 2,941,434

PHOTOELECTRIC SCANNING DEVICE FOR GENERATING MUSICAL'TONES Filed Oct.31, 1955 6 Sheets-Sheet 1 INVENTOR. Ma mu- 624041 J0.

ITTOP/Viff June 21, 1960 M. CLARK, JR 2,941,434

PHOTOELECTRIC SCANNING DEVICE FOR GENERATING MUSICAL TONES 6Sheets-Sheet 2 Filed Oct. 31, 1955 INVENTOR fizzy/.44: (2404 8% J i June21, 1960 M. CLARK, JR

PHOTOELECTRIC SCANNING DEVICE FOR GENERATING musrcm. TONES 6sheets-sheet 3 Filed Oct. 31, 1955 INVEN TOR. [Var/u: 62424, ./2

June 21, 1960 M. CLARK, JR 2,941,434

PHOTOELECTRIC SCANNING DEVICE FOR GENERATING MUSICAL TONES 6Sheets-Sheet 4 Filed Oct. 31, 1955 FIG-9 W H, w 4

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INVENTOR. New: 6442 .4 WJJJJ June 21, 1960 M. CLARK, JR 2,941,434

PHOTOELECTRIC SCANNING DEVICE FOR GENERATING MUSICAL TONES Filed Oct.31, 1955 6 Sheets-Sheet 5 fla /a: Cum; J2.

M. CLARK, JR PHOTOELECTRIC SCAN 2,941,434 NING DEVICE FOR GENERATINGMUSICAL TONES June 21, 1960 6 Sheets-Sheet 6 Filed 001:. 31, 1955INVENTOR. MIA V/Mi 62494, W M

United States Patent PHOTOELECTRIC SCANNING DEVICE FOR GENERATINGMUSICAL TONES Melville Clark, In, Boston, Mass. (Dept. of ChemicalEngineering, Massachusetts Institute of Technology, Cambridge 39, Mass.)

Filed Oct. 31, 1955, Ser. No. 543,948

Claims. (Cl. 84-118) and easily be interchanged for voicing theinstrumentthat is, for changing the timbres or tone colors which theinstrument is capable of producing.

Still another object is to provide improved means for scanning themodulation tracks of a photoelectric musical instrument.

Other objects and advantages of the invention will appear as thedescription proceeds.

Briefly stated, in accordance with one aspect of this invention, aphotoelectric musical instrument has a stationary member carrying aplurality of modulation tracks each having an optical transmittance thatvaries along its length in accordance with a musical tone. Themodulation tracks are preferably arranged in a coplanar array consistingof rows of linearly alined end-to-end tracks representing tones ofsimilar timbre but diiferent pitch, and of columns of parallelside-by-side tracks representing tones of similar pitch but differenttimbre. The in strument can produce as many different basic timbres asthere are rows of modulation tracks, and it can produce a much largernumber of composite timbres or tone colors by combining the basictimbres in different proportions. The stationary member may be removedand replaced by a similar member carrying a different set of modulationtracks for changing the basic timbres or tone colors of the instrument.

A plurality of cylindrical scanners are provided, one for each column ofmodulation tracks, which moves light beams repetitively alongthe lengthsof the tracks to produce light modulated in accordance with musicaltones. The scanning cylinders are rotated at different speeds so thatthe different rows of tracks produce tones of different ptiches. Aplurality of keying shutters are provided, one for each column oftracks, for selecting the pitch of the tone to be produced.Photoelectric transducer means convert the modulated light into electricsignals, which may be used to produce sound waves.

The invention will be better understood from the following dmcriptiontaken in connection with the accompanying drawings, and its scope willbe pointed out in the appended claims. In the drawings,

Fig. 1 is a simplified schematic and circuit diagram of a photoelectricmusical instrument embodying principles of this invention;

Fig. 2 is a schematic representation showing operating 2,941,434Patented June 21, 196 0 principles of a cylindrical scanner used in thesame musical instrument;

Fig. 3 is another schematic representation showing operating principlesof the same scanner;

Fig. 4 is a schematic plan view, partly in section, illustrating theoptical system of the same musical instru ment;

Fig. 5 is a section taken generally along the line 5-5 of Fig. 4;

Fig. 6 is a detail of one keying shutter in the same musical instrument;

Fig. 7 is a fragmentary detail showing schematically a portion of astationary member carrying a plurality of modulation tracks for the samemusical instrument;

Fig. 8 is a section taken generally along the line 88 of Fig. 7;

Fig. 9 is a schematic illustration of apparatus forrotating the scanningcylinders of the same musical instrument;

Fig. 10 is a schematic fragmentary plan view, partly in section, showinga portion of an alternative optical system using scanning cylinders of adifferent type;

Fig. 11 is a schematic fragmentary plan view, partly in section, showinga modification of the alternative optical system;

Fig. 12 is a schematic plan view, partly in section, showing anotheralternative optical system using scanning cylinders of still anothertype; and

Fig. 13 is a circuit diagram showing an electric circuit and timbreadjustment means associated with photo electric transducers of theoptical system shown in Fig. 12.

Reference is now made to Fig. 1 of the drawings, which is a schematicrepresentation of a photoelectric musical instrument embodyingprinciples of the present invention. In Fig. 1, only one cylindricalscanner and keying shutter is shown, but it will be understood that aplurality of such scanners and shutters will be provided in actualpractice (as is shown in subsequent figures of this application) forproducing tones of ditferent pitch. A light source includes a pluralityof electric lamps 1, 2 and 3, there being one lamp for each basic timbreto be produced by the instrument. Any desired number of such lamps maybe provided to produce any desired number of basic timbres or tonecolors. These lamps illuminate a plurality of optical apertures 4, 5 and6, which preferably are linearly alined, long, narrow optical slits.Apertures 4, 5 and 6 produce a plurality of light beams directed to ascanning cylinder 7 which may be a transparent prism continuouslyrotated at a constant speed by a motor 8. The rotational axis ofcylinder 7 is parallel to slits 4, 5 and 6.

A keying shutter 9 is linked to a key 10 which may be one key in a pianoor an organ-type manual keyboard. or may be a pedal in an organ-typepedal clavier. Keying shutter 9 carries a plurality of optical apertures11, 12 and 13, which preferably are parallel optical slits each having alength extending normal to the plane of the drawing-that is, transverseto a projection of the axis of cylinder 7 upon the plane of the keyingshutter 9. Light passing through apertures 11, 12 and 13 crosses aplurality of modulation tracks 14, 15 and 16 carried by a stationarymember 17, and light transmitted by the modulation tracks reaches thecathode of a photoelectric transducer 18, preferably a phototube or aphotomultiplier tube, which converts modulated light into an electricsignal.

Modulation tracks 14, 15 and 16 are coplanar and parallel, side-by-side,and each has a length extending in a direction normal to the plane ofthe drawing. Each track has an unmodulated section (preferably opaque)and at least one modulated section with an optical trans,

mittance which varies along its length in accordance with a musicaltone. Each modulated section generally comprises a large integral numberof wavelengths of the fundamental frequency. The modulation tracks maybe multisection tracks of the type described in my copending patentapplication entitled Progressively Keyed Electrical Musical Instrument,Serial No. 543,949, filed October 31, 1955.

As scanning cylinder 7 rotates, the three light beams passing throughapertures 4 5 and 6 are moved repetitively along the lengths of tracks14, 15 and 16. in the normal rest or unkeyed position of shutter 9,apertures 11, 12 and 13 are in alinement with unmodulated sections ofthe modulation tracks and no modulation of the light occurs. In otherwords, shutter 9 normally blocks the optical paths passing throughmodulated sections of the tracks 14, 15 and 16. When key 10 isdepressed, shutter 9 moves upward and apertures 11, 12 and 13 are movedinto alinement with modulated sections of tracks 14, 15 and 16 so thateach light beam is modulated in accordance with the musical tonerepresented by a corresponding one of the modulation tracks.

Since light from all three beams reaches transducer 18, the electricsignal produced by transducer 1% represents a composite tone that is thesum of the basic tone colors represented by the modulation of thetracks. The timbre or tone color of the composite tone is controlled byadjusting the relative amounts of light transmitted along the threescanning beams in a manner hereinafter more fully explained. Variousmodifications of the keying shutter 9 and preferred types of linkagebetween shutter 9 and key 10 are described in my copending patentapplication, Serial No. 543,949, hereinbefore identified. In a simplemusical instrument, shutter 9 may be linked to key 10 by a directmechanical connection.

Electric power is supplied to phototube 18 by any suitable means, suchas battery 19. The electric signal produced by phototube 18 is amplifiedby an amplifier 20, and itsamplitude is adjusted by a volume controlwhich may,-for example, consist of a resistance-type voltage divider 21having an adjustable tap 22 linked to a swell pedal 23 for controllingthe overall loudness of the musical tone produced by the instrument.

Signal modifiers 24 may be provided if desired for adding variousmusical effects, such as reverberation, vibrato and tremolo eifects,choral effects and the like. For this purpose, signal modifiers of typespresently known to those skilled in the artmay be employed. For example,a reverberation device may be constructed in accordance with principlesdisclosed on pages 522 and 523 of the book Elements of Sound Recordingby John G. Frayne and Halley Wolfe, published by John Wiley and Sons,lnc., New York, 1949. After further amplification by an amplifier 25 theelectric signal is supplied to one or more loudspeakers 26 which convertthe electric signal into sound waves.

Individually adjustable amounts of electric current are supplied to eachof the lamps 1, 2 and .3, by a lamp-energizing and stop ortimbre-control system which will now be described. Alternating currentis supplied to loads 27 and 28 by any suitable means such as acommercial 60 cycle electric outlet. Leads 27 and 23 supply electriccurrent to motor 8, which may be a synchronous electric motor forrotating the scanning cylinders at constant predetermined speeds. Leads27 and 2% are also connected to the primary 29 of a transformer having atapped secondary 30 connected to a plurality of distribution lines 31,32, 33 and 34. Distribution line 31 is a common line which is connectedto one terminal of each of the lamps 1, 2' and 3. Lines 32, 33 and 34are connected to different taps of secondary 30, so that differentvalues of alternating voltages are present between line 31 and each ofthe lines 32, 33 and 34.

Other terminals of lamps 1, 2 and 3 are connected to a plurality ofindividually adjustable selector switches 35, 36 and 37, as shown. Eachof the selector switches has three taps which are connected torespective ones of the distribution line 31. Selector switches 35, 36and 27 may either has no electrical connections or is connected todistribution line 31. Selector switches 35, 36 and 37 may be connectedto drawbars, dials, or any other adjustment devices that can be operatedconveniently by the musician, and are individually adjustable forcontrolling the relative amounts of electric current supplied to lamps1, 2 and 3. These in turn control the relative brightnesses of the threelamps, and thus control the proportions of the three basic timbres thatenter into the composite timbre of the musical tone produced by theinstrument. Preferably, the transformer taps are so spaced as to provideequal loudness increments between successive adjustment positions at theselector switches.

The amount of hum produced by exciting the lamps with alternatingcurrent can be made negligible and other advantages can be obtained byusing low voltage incandescent lamps-6 volt lamps, for exa1nplewhichhave relatively heavy filaments and consequently do not change intemperature or brightness appreciably during an alternation of thesupply current. However, if desired, means may be provided for supplyinglamps 1, 2 and 3 with direct current or with high frequency alternatingcurrent to eliminate any possibility of hum from this source.

The composite timbre or tone color of the tone produced by theinstrument may be controlled in ways other than by controlling therelative amounts of current supplied to the lamps. For example, thethree lamps may have constant brightnesses, or a single lamp may beused, and optical wedges or the like may be employed to control therelative amounts of light transmitted in the three beams. As anotheralternative, separate photoelectric transducers may be provided for eachbeam to produce separate signals for each of the basic timbres; and therelative amplitudes of these signals can then be controlled by anysuitable volume control apparatus for adjusting the composite timbre ofthe tone. The latter alternative is illustrated in Figs. ll and t2, andis more fully de scribed hereinafter. The swell pedal 23 mayv also belinked to an optical wedge for controlling the over-all amount of lightreaching transducer 18, or the swell pedal may control apparatus forvarying the amount of current supplied to all of the lamps 1, 2 and 3.

Reference is now made to Figs. 2 and 3, which illus trate the principleof a transparent prism-type of cylindrical scanner. A mask 38 carries anentrance aperture 4 of the scanning system. Aperture 4 preferably is along narrow optical slit parallel to the longitudinal or rotational axisof scanning cylinder 7. Aperture 4 is illuminated in a mannerhereinafter more fully explained to form a narrow beam. of lightrepresented in the drawing by broken line 39. Scanning cylinder 7 is aregular prism of transparent material having a large refractive index,such as pure cast methyl methacrylate, although other transparentmaterials including glass may be employed. Cylinder 7 is continuouslyrotated at constant speed about its longitudinal axis by suitablecoupling to a driving motor. The transverse section of cylinder 7 is aregular polygon having an even number of sides.

Referring particularly to Fig. 2, light beam 39 enters one face ofcylinder 7 and is deflected laterally with respect to the cylinder by anamount and in a direction which is a function of the angular position ofthe scanning cylinder. The light beam emerges from. the opposite face ofthe scanning cylinder, as is indicated at 40. Since the cylinder has atransverse section that is a regular polygon having an even number ofsides, the opposite faces of cylinder 7 are parallel. Consequently, thelight beam emerging from the cylinder at 40 is always substantiallyparallel to the light beam entering the cylinder at 39, but is movedrepetitively from side to side as the cylinder rotates. For example, ifcylinder 7 rotatesin a clockwise direction, the emerging beam movesrepetitively from right to left as viewed in Figs. 2 and 3. 1

Whenever cylinder 7- reaches an angular positionsuch that beam 39strikes the edge of a dihedral angle of the prism, as shown in Fig. 3,the beam is split into two parts 40 and 40'. Upon further clockwiserotation of cylinder 7, beam 40 is extinguished and beam 40' is moved inthe right-to-left direction until beam 39 strikes the edge of the nextdihedral angle of the prism.

As the scanning cylinder rotates, beam 40 moves transversely across thekeying shutter 9 carrying an optical aperture 11 which preferably is along narrow optical slit extending in a direction transverse to thelongitudinal axis of cylinder 7. A small portion of beam 40 passesthrough aperture 11 and is moved repetitively along the length ofmodulation track 14.

When shutter 9 is in its normal rest or unkeyed position, the lightpassing through aperture 11 reaches an unmodulated section of track 14and no modulation of the light is produced. However, when the key linkedto shutter 9 is depressed, aperture 11 is moved transversely withrespect to track 14, and the light beam is moved repetitively along thelength of a modulated section of the track. As this happens, modulatedlight is transmitted to photoelectric transducer 18 which thereuponproduces an electric signal corresponding to the musical tonerepresented by the modulation of the track.

Although the beam scans the modulation track in a somewhat non-linearmanner, that is, the beam moves at a different speed along the centerlengthwise portion of track 14 than it moves along end portions of thetrack, this non-linearity can be compensated by a correspondingnon-linearity in the modulation of the track, by making the modulationtracks from recordings scanned by similar optical systems, for example.In this way distortion of the musical tones due to scanningnon-linearities can be avoided.

Figs. 4 and show the optical system of the improved photoelectricmusical instrument. The optical system shown includes twelve scanningcylinders associated with twelve columns of modulation tracks, which mayprovide tones of twelve different pitches corresponding to the twelvesemitones in one octave of the tempered musical scale. The number ofdifferent pitches that can be produced may be increased by acorresponding increase in the number of scanning cylinders andassociated columns of modulation tracks, either by extending the lengthof the optical system shown or by adding other similar optical systems.Alternatively, the number of different pitches may be increased byproviding modulation tracks representing more than one pitch in eachcolumn. For example, harmonically related pitches may be generated by aplurality of modulation tracks that are scanned at the same rate, but inwhich the optical transmittances of the several tracks are modulatedwith different integral numbers of the fundamental wavelength. For thelatter alternative, the keying shutters would be divided into two ormore parts connected to different keys.

A light source includes three lamps 1, 2 and 3 respectivelyassociatedwith three different rows of modulation tracks for producing threedifferent basic timbres of each pitch. By adding additional lamps andadditional rows of modulation tracks, any desired number of basictimbres may be provided.

The three lamps 1, 2 and 3 are enclosed in separate lamp housings whichcommunicate with respective ones of three input light chambers 41, 42and 43, which are generally parallel and are arranged in a stack as isbest shown in Fig. 5. Chambers 41, 42 and 43 are separated from oneanother by dividers 44 and 45. The spacing of the input light chamberscorresponds to the spacing of the rows of modulation tracks. Preferably,each row of modulation tracks is approximately one centimeter wide, andaccordingly each input light chamber has a depth of substantially onecentimeter. Since lamps 1, 2 and 3 require a space larger than onecentimeter in depth, the lamps are staggered in the manner shown in Fig.4 so that .the lamp housings may have a depth greater than that of theindividual light chambers.

The filament of lamp 1 is located at the principal focus of asubstantially parabolic mirror 46 which collimates light produced bylamp 1 and directs it in a beam parallel to the row of scanningcylinders. In a similar manner, light produced by lamp 2 is collimatedby a mirror 47, and light produced by lamp 3 is collimated by a mirror48. Each of these collimated beams is reflected from a plurality ofdistribution mirrors, identified in the drawing by reference numerals 49through 60, arranged in a stepwise array across and along the collimatedbeam, as shown in Fig. 4, and each oriented at an angle of substantially45 degrees to the direction of the collimated light. Preferably thesedistribution mirrors are reflecting surfaces of an integral step-likemember 61 and are similar to the distribution mirrors more fullydescribed in my copending patent application entitled Multi-ToneElectrical Musical Instrument, Serial No. 543,865, filed October 31, 1955 The distribution mirrors reflect light from the collim'ated beams toilluminate a plurality of apertures, such as aperture 4, carried by astationary mask 38. These apertures are the entrance apertures of thescanning system. In general, each input light chamber has one suchaperture for each of the scanning cylinders. For example, there may bethree vertical slit-like apertures 4, 5 and 6, linearly alinedend-to-end in mask 38, associated with scanning cylinder 7 in the mannerindicated in Fig. 1, there being one of these apertures for each of theinput light chambers 41, 42 and 43. Similarly, there are threeapertures, 62, 63 and 64, associated with the scanning cylinder 65 as isshown in Fig. 5.

A stationary member 17, parallel to mask 38, carries a coplanar array ofmodulation tracks arranged in a plurality of rows of linearly alinedend-to-end tracks and a plurality of columns of parallel side-by-sidetracks. There is one row of modulation tracks for each of the threeinput light chambers, and there is one column of modulation tracks foreach of the twelve scanning cylinders. Each of these tracks has :amodulated section with an optical transmittance that varies along itslength in accordance with a different musical tone. In the preferredarrangement, each row of tracks represents similar timbres of differentpitch, while each column of tracks represents different timbres ofsimilar pitch. Accordingly, in the arrangement illustrated there arethree different basic timbres for each of the twelve different pitchesin a musical octave.

The twelve scanning cylinders, such as cylinders 7 and 65, are arrangedin a row between mask 38 and the member 17 carrying the modulationtracks. These scanning cylinders are continuously rotated at differentconstant speeds so that the modulation tracks in different rows arerepetitively scanned at different rates to produce musical tones ofdifferent pitch. There is a column of three modulation tracks associatedwith each scanning cylinder to produce musical tones having differentbasic timbres.

For example, modulation tracks 14, 15 and 16 are associated with andoptically scanned by cylinder 7, while modulation tracks 66, 67 and 68are associated with and optically scanned by cylinder 65.

There is a keying shutter associated with each of the scanningcylinders. For example, keying shutter 9 is associated with cylinder 7,and keying shutter 69 is associated with cylinder 65. In their normal orunkeyed positions, these shutters block the optical paths throughmodulated sections of the tracks carried by member 17, so that nomodulated light reaches the photo-electric transducer 18. However, eachshutter is connected to an individual-1y operable key of a keyboard, sothat when any selected one of the keys is depressed a correspondingshutter is raised to bring a plurality of optical aperturessimultaneously into alinement with modulated sections of the threemodulation tracks in one row. Modulated light is thus produced that ismodulated in accordance with three different basic timbres of a selectedpitch,

and gransdu'cer 18 produces an electric signal representing a compositetimbre of the selected pitch. The character of this composite timbre iscontrolled by adjusting the relative brightnesses of lamps 1, 2 and 3 inthe manner hereinbefore explained.

Light transmitted by the modulation tracks enters a single output lightchamber 70 and is collected by a mirror 71 which directs such light to acathode of photoelectric transducer 18. For best optical efficiency,mirror 71 is arranged to form an image of all the modulation tracks uponthe cathode of transducer 18.

The various optical parts are mounted within, and are held in positionby, a rigid frame 72 which may, if desired, be hermetically sealed toexclude dust and other foreign materials. The light chambers may befilled up with any transparent material, such as air, other transparentfluids, or transparent solid materials. Light pipes, lenses, or otheroptical elements may be used in place of mirrors.

With particular reference to Fig. 5, each of the scanningcylinders-cylinder 65, for examplemay be a prism of solid transparentmaterial supported at each of its ends by end caps 73 and 74 connectedto shafts 75 and 76 which rotate in bearings secured to frame 72. Shaft76 may be the driving shaft for the scanning cylinder, and it iscontinuously rotated at a constant speed by means hereinafter described.Each of the keying shutters, shutter 69, for example, is biased to itsnormal or unkeyed position by a small spring 77, and is linked to a keythat may be depressed to move the shutter upward for permitting light topass through the shutter apertures to modulated sections of themodulation tracks.

Member 17, which carries the modulation tracks, may be lifted out offrame 72 and replaced with a similar member carrying differentmodulation tracks for changing the basic timbres which the instrument iscapable of producing. In this way a small instrument capable ofproducing only a relatively small number of basic timbres can be veryversatile, since the basic timbres, or voicing, can be changed wheneverdesired by replacing the modulation tracks with other tracksrepresenting a dif ferent set of musical tona-lities.

A detail of keying shutter 69 is shown in Fig. 6. The shutter isgenerally opaque, but has three transparent optical apertures 78, 79,and 80. These apertures, as well as other apertures of the opticalsystem, preferably are transparent portions of a generally opaque stripof photographic film or the like supported by a frame of metal or otherdurable rigid material, as is more fully discussed in my copendingpatent application Serial No. 543,865 hereinbefore identified. An upperportion 81 of the keying shutter is linked to a key in a keyboard of theinstrument.

Fig. 7 is a schematic representation of a portion of the coplanar arrayof modulation tracks. Member 17 carries a plurality of modulationtracks, such as tracks 14, 15, 16, 66, 67 and 68. Preferably each trackhas an unmodulated section, presented in the drawings by heavy solidshading at the bottom of each track, with which the apertures of thekeying shutter are alined when the keying shutters are in their normalor unkeyed positions. Each track also has one or more modulatedsections, represented inthe drawing by stippled shading, in which theoptical transmittance of the track varies along its length in accordancewith a musical tone. Preferably these modulated sections are of thevariable density type, although variable-area or other types ofmodulation tracks may be employed under certain circumstances.Generally, the use of variable-area tracks or the like requires morecomplex keying systems to avoid excessive distortion.

The modulation tracks are arranged in a plurality of rows and columns.For example, tracks 14 and 66 are in the same row, and tracks 14, 15, 16are in thesame column. Preferably each track in a given columnrepresents a different timbre of similarpitch; and these timbrescorrespond to the timbres or tone colors of dif ferent musicalinstruments or groups of instruments. For example, one row of tracks mayproduce tones that simulate the tones of a violin, another row of tracksmay produce tonesv that simulate the tones of a trumpet, and a third rowof tracks may produce tones that simulate tones of a flute. However,instead of simulating the tone colors of individual instruments, othertone. colors may be represented and other arrangements of the tracksemployed in a manner more fully described in my copending patentapplication Serial No.543,865, hereinbefore identified, it beingunderstood that each tone disc in the apparatus of said copendingapplication corresponds to one column of modulation tracks in theapparatus of the present application. V

Fig. 8 is a section showing 'a'preferred construction of the stationarymember carrying the modulation tracks.- A flat transparent plate 17, ofglass or other suitable material, is parallel to another similar plate17'. Between these two plates, in a sandwich-like construction, is afilm or photographic emulsion 82, different areas of which differ inoptical transmittance to form the array of modulation tracks. In actualpractice the tracks may be formed upon film 82 by photographic means,printing, or in any other suitable manner, and preferably they arephotographically reproduced from a set of master tracks made, forexample, using sound-on film recording techniques, from recordings oftones produced by the instruments that are to be simulated. Toprotect'thc film 82 and to prevent shrinkage or other damage, plates 17and 17' are preferably hermetically sealed together by any suitablesealing means 83.

Reference is now made to Fig. 9 which shows a pre ferred arrangement forcontinuously rotating the scan: ning cylinders. Each cylinder isconnected to a driving shaft, such as shaft '76, carrying a drivingwheel. The twelve driving wheels which are connected to respective onesof twelve scanning cylinders are identified in the drawing by referencenumerals 84 through inclusive. These driving wheels have differentdiameters, so that the different scanning cylinders are driven atdifferent constant speeds. Preferably the diameter of each driving wheelis related to the diameter of the next adjacent driving wheel by a ratioequal to the twelfth root of two, so that the fundamental frequencies ofthe tones produced by adjacent rows of modulation tracks have a ratioequal to the twelfth root of two. In this manner the twelve pitches ofthe instrument are properly related to the twelve semitones in an octaveof the equaltempered musical scale.

The driving wheels 84 through 95 are continuously rotated at differentconstant speeds by an endless belt 96, which is in contact with alltwelve of the driving Wheels and with a driving pulley 97 linked to thedriving motor 8. To keep the belt taut, an idler pulley 98 is mounted onan arm 99 pivoted at 100 and urged down.- ward by a spring 161. To keepthe belt in good con tact with all of the driving wheels a-plurality ofidler pulleys, identified in the drawing by reference numerals 102through 1% are positioned between adjacent pairs of the driving wheelsin the manner shown. In a large instrument covering many octaves,several such belt and pulley systems may be used, one for each ofseveral groups of scanners, with driving pulleys driven at differentspeeds. I

Reference is now made to Fig. 10, which shows a portion of analternative optical system using mirror-type rotating scanningcylinders. Parts identical to those in the embodiment hereinbeforedescribed are identified by the same reference numerals. The input lightsystem is generally similar to that described in connection with Fig. 4except that only half as many distribution mir rors are required. Thedistribution mirrors"107, 108, and 109 are positioned along and across a'collimated light beam from a light source (not shown), and illuminate aplurality of optical apertures 110, 111, and -112 which are entranceslits for the scanning system. It will be noted that only one entranceslit is provided for each pair of scanning cylinders. The entrance slitsdefine beams of light that pass between the scanning cylinders of eachpair, and are each divided into two parts by V- shaped beam-splittermirrors 113, 114, and 115 which direct light to each of the scanningcylinders. For example, beam splitter 113 directs light to scanningcylinders 116 and 117, beam splitter 114 directs light to scanningcylinders 118 and 119, and beam splitter 115' directs light to scanningcylinders 120 and 12 1.

' The transverse sections of the scanning cyhnders are preferablyregular polygons, and the surfaces of the scanning cylinders are mirrorsor other reflecting surfaces. The scanning cylinders are continuouslyrotated at different constant speeds so that the modulation trackscarried by member 17 are repetitively'scanned in the manner hereinbeforeexplained. A plurality of keying shutters, such as shutter 69, areprovided, one for each scanning cylinder. The keying shutters may beidentical to the keying shutters described in connection with Fig. 4.

Unlike the transparent-prism type scanners, the mirror type scannersproduce emergent light beams which in general are not parallel to theentering beams or to each other. These beams can be collected moreefi'iciently with a simpler optical system if they are first madeparallel or collimated. For this purpose there is provided a pluralityof cylindrical lenses identified in the drawing by reference numerals122 through 127. For economy and convenience in manufacture and assemblyof the instrument, lenses 122 through 127 preferably are molded from acontinuous strip of transparent plastic so that all of the collimatinglenses can be assembled in the optical system as an integral unit. Thecollimated light beams are collected by mirror 71 and directed to thecathode of a photoelectric transducer (not shown) in the same manner aswith the apparatus illustrated in Fig. 4.

Alternatively, instead of the curved light-collecting mirror 71, astaggered array of mirrors may be used in the output light chamber, asshown in Fig. 11, in an arrangement analogous to the array ofdistribution mir rors in the input light chamber. Lenses 122 through127, which correspond to and replace mirrors 122 through 127, aredesigned to focus light from the modulation tracks upon respective onesof the mirrors 128 through 133 in this staggered array, from which thelight is directed through a collecting lens 134 or the like to thecathode of the phototube 135. Preferably the mirrors in array 128through 133 most distant from the modulation tracks are also the onesmost distant from.

the collecting lens so that the range of sweep of the light beams isminimized. The mirrors 128 through 133 are not necessarily oriented atexactly forty-five degrees relative to the plane of track-carryingmember 17, but are oriented to direct the light to appropriate portionsof lens 134 for transmitting the modulated light to the phototubecathode. I

Reference is now made to Fig. 12 which illustrates another alternativeoptical system. In this system there is a single input light chamber 136for all of the different timbers, and a plurality of output lightchambers 137, 138 and 139, there being a separate output light chamberfor each row of modulation tracks. A single light source is employedwhich may, for example, be an elongated tubular fluorescent lamp 140, ormay be some other type of long distributed light source. The-length ofthe light source is greater than the total distance between the firstand the last scanning cylinders. As a further aid in securing a longdistributed light source of uniform brightness, an optical diffusingplate 141 may be positioned in the input light chamber in the mannershow of diametric slots in the opaque cylinders. Alternatively, thescanning cylinders may be in the form of hollow cylindrical drums havinga generally opaque surface provided with a plurality of diametricallyalined transparent apertures. Diifused light from the input lightchamber 136 can travel through the scanning system only along directionsestablished by the diametrically alineda Consequently, as:

apertures of the scanning cylinders. each scanning cylinder rotates alight beam is moved repetitively along the length of one row ofmodulation.

tracks carried by stationary member 17.

- A plurality. of keying shutters, such as shutter 69,. operate in themanner described in connection with: Fig. 4 to direct these light beamseither to unmodulatedl or to modulated sections of the modulationtracks, selectively. The light beams that pass through the mod-- ulationtracks are collimated by a plurality of cylindricali lenses, such aslens 143, and the collimated light is collooted by a mirror 144.

Light passing through the upper row of modulation tracks enters outputlight chamber 137, and is directed by mirrors 144 and 145 to the cathodeof a photoelectric transducer 146. Light passing through the center rowof modulation tracks enters output light chamber 138 and is directed bymirrors 144 and 147 to the cathode of a photoelectric transducer 148.Light passing through the bottom row of modulation tracks enters outputlight chamber 139 and is directed by mirrors 144 and 149 to the cathodeof a photoelectric transducer 150. Transducers 146, "148 and 150'respectively, produce three electric signals, each representing adifferent basic timbre of the selected pitch.

' For controlling the timbre of the composite musical tone, a circuitsuch as that shown in Fig. 13 may be used. to adjust the relativeamplitudes of the three signals: produced by transducers 146, 148 and150. Transducers: 146, 148 and 150, which may be phototubes or photo--multiplier tubes, receive direct current electric power from a suitablesource such as battery 151. The photo-- tubes are connected as shown toselector switches 152,. 153 and 154, each of which has a plurality ofcontacts: connected to respective ones of bllSses or lines 155, 156,.157 .and 158 leading to exponentially-spaced taps on the primary of atransformer 159. The secondary of trans-- former 159 is connected to theinput of amplifier 20 so that electric signals from different ones ofthe busses are transmitted with diflerent degrees of amplification. Theproportion of each basic timbre in the composite tone is controlled byindividually adjusting the three selector switches .152, 153 and 154,which thus constitute a stop system of the musical instrument. Theoutput of amplifier 20 may be connected to a circuit similar to thatshown in Fig. l.

In all of the embodiments described-various permutations in the order orpositions of elements of the optical systems may be made. For example,the keying shutters may be placed on either side of the modulationtracks, and so may the strip or row of lenses. Also, the positions oflight sources and photoelectric transducers may be transposed so thatlight travels through the optical systems in the reverse direction tothat described.

It should be understood that this invention in its broader aspects isnot limited to specific embodiments herein illustrated and described,and that the following claims are intended to cover all changes andmodifications that do not depart from the true spirit and scope of theinvention.

What is claimed is:

1. In an electrical musical instrument, the optically alined combinationof a stationary source of light, a stationary photoelectric transduceroptically alined with said. sourcefor receiving such light andconverting, variations therein to electric signals, a stationary,light-transmissive, flat plate disposed optically in alinement betweensaid source and said transducer, said plate carrying thereon, inparallel, side-by-side relation, a variable-density, photographic soundtrack and an unmodulated strip, said variable-density track beingmodulated in its longitudinal direction with a variable-densityrepresentation of. a musical tone, a continuously rotative scanningdevice disposed optically in alinement between said source and saidtransducer, said scanning device being in optically alined operativeassociation with said sound track and strip and being operable to scanin'said longitudinal direction said sound track and said striprepetitively and continuously, a reciprocative shutter disposedoptically in alinement with and between said source and said transducer,a playing key, and a mechanism linking said playing key to said shutterfor direct control of the reciprocation thereof, said shutter being agenerally opaque, fiat ribbon parallel and adjacent to said plate, saidribbon containing a light-transmissive slit parallel to saidlongitudinal direction of the sound track and at least equal in lengthto the longitudinal dimension of said sound track,

said ribbon and slit being reciprocatively movable transverse to saidlongitudinal dimension by action of said playing key, said slit being inoptical alinement with said unmodulated strip when the playing key isreleased and being moved as the playing key is depressed. into opticalalinement with said sound track, said slit being parallel to saidlongitudinal direction of said sound track at all times so that theentire length of the track is always equally exposed to scanning by thescanning device, irrespective of whether said key is wholly or onlypartially depressed.

2. The combination claimed in claim 1, wherein said scanning devicecomprises a prism disposed optically between said source and said plate,with its longitudinal axis parallel to said plate and the projection ofsaid axis on said plate perpendicular to the longitudinal direction ofsaid sound track and said unmodulated strip, a generally opaque,stationary member having a lighttransmissive slit disposed opticallybetween said source and said prism with such slit parallel to thelongitudinal axis of the prism, and mechanism for continuously rotatingsaid prism at constant speed about its longitudinal axis.

3. The combination claimed in claim 1, wherein said scanning devicecomprises a prismoidal mirror disposed optically between said source andsaid plate, with its longitudinal axis parallel to said plate and theprojection of said axis on said plate perpendicular to the longitudinaldirection of said sound track and said unmodulated strip, a generallyopaque, stationary member having a lighttransmissive slit disposedoptically between said source and said mirror with such slit parallel tothe longitudinal axis of the prismoidal mirror, and mechanism forcontinuously rotating said p-rismoidal mirror at constant speed aboutits longitudinal axis.

4. The combination claimed in claim 1, wherein said scanning devicecomprises a generally opaque drum having therein a plurality oflight-transmissive, diametric slits, said drum being disposed opticallybetween said source and said plate, with its longitudinal axis parallelto said plate and the projection of said axis on said.

plate perpendicular to the longitudinal direction of said sound trackand said unmodulated strip, and mechanism 12 for continuously rotatingsaid drum at constant speeda-bou't its longitudinal axis.

5. In an electrical musical instrument, the combination of a stationary,light-transmissive, flat plate carrying thereon a plurality ofvariable-density photographic sound tracks of equal longitudinaldimensions arranged in an array of rows and columns, said tracks beingmodulated in their longitudinal directions with representations ofdifferent musical tones, the tracks in each column bein parallel andrepresenting the same note in difierent timbres, the tracks in each rowbeing in linear alinement and representing different notes of similartimbre, said plate also carrying thereon a plurality of unmodulatedstrips, one adjacent and in parallel, side-by-side relation to each ofsaid sound tracks, a plurality of reciprocative shutters, one disposedadjacent to and in optical alinement with each column of said soundtracks, each shutter including a generally opaque, fiat ribbon havingtherein a plurality of parallel, light-transmissive, transverse slits,each equal in length to the longitudinal dimension of each sound track,with the transverse spacing between said slits equal to the transversespacing between the rows of sound tracks, whereby all slits of theshutter are movable into simultaneous optical alinement with the entirelongitudinal lengths of all sound tracks of a column or all unmodulatedstrips of a column, selectively, a keyboard comprising a plurality ofplaying keys, means operatively linking each of said keys to arespective one of said shutters, so that depression of each key movesthe as-.

sociated shutter slits into optical alinement with the entirelongitudinal lengths of all the sound tracks in a respective column, aplurality of lamps, one for each of said rows, a generally opaque, flatplate containing a plurality of parallel, light-transmissive slitsdisposed to be illuminated by said lamps, each lamp illuminating adifferent lengthwise portion of each slit, forming a plu rality ofribbons of light each comprising light rays from each lamp, a pluralityof continuously rotative scanning devices, one for each of said columns,for deflecting respcctive ones of said ribbons of light repetitively andcontinuously along the length of all the sound tracks in the respectiveone of said columns, the rays from each lamp being confined to thetracks in a respective one of said rows, means for rotating saidscanning devices at different speeds respectively proportional to thefundamental frequencies of the notes of a musical scale, a photoelectrictransducer disposed to receive light transmitted through said soundtracks and to convert variations thereof into electric signals, wherebythe depression of any one of said playing keys results in the productionof an electric signal corresponding to a musical tone having the pitchrep-resented by the position of that key in the keyboard, and means .ioradjusting the relative brightness of said lamps for varying the timbreof the musical tone so pro duced.

References Cited in the tile of this patent UNITED STATES PATENTS1,747,791 Peterson Feb. 18, 1930 1,850,267 Henroteau Mar. 22, 19322,169,842 Kannen berg Aug. 15, 1939 2,222,937 Dimmick Nov. 26, 19402,439,392 Jones Apr. 13,1948 2,484,381 Fuschi Oct. 18, 1949 2,506,599Jordan May 9 1950 2,540,285 Philips Feb. 6, 1951

